Phagocytosis (phagocytic action) is cellular endocytosis (intracellular incorporation) which acts not only against exogenous foreign substances such as bacteria, viruses, and dusts, but also acts against foreign substances that occur in the living body (unwanted substances), such as dead cells, oxidized LDL, and denatured proteins. Elimination of foreign substances by phagocytes such as macrophages and neutrophils plays an important role in the homeostatic maintenance,
On the other hand, there is known a decrease in homeostatic function due to a decline of phagocytic capacity. For example, there are a report that delay of wound healing due to aging is correlated with a decreased phagocytic function of macrophages infiltrating into wound areas (Journal of Investigative Dermatology, 2001, Vol. 117, pp. 1027 to 1035), a report that in bacterial pneumonia due to aging, a decrease in the phagocytic capacity of migrating neutrophils is associated with susceptibility to infections (Mechanisms of Ageing and Development, 2001, Vol. 122, pp. 1899 to 1913), a report showing a decrease in amyloid-β phagocytosis of brain phagocytes (microglia) with aging (Pharmacology & Therapeutics, 2013, Vol. 139, pp. 313 to 326), a report that an elimination of amyloid-β is increased by enhanced microglial phagocytosis (Nature Medicine, 2001, Vol. 7, pp. 369 to 372), and the like. Based on these reports, an ability of phagocytes to eliminate foreign substances (phagocytic capacity) may serve as an indicator for facilitation of wound healing, an ability to prevent against infections, maintenance of brain function, or the like. It has been reported that phagocytic capacity of phagocytes (monocytes) in human peripheral blood is decreased with aging (AIDS, 2012, Vol. 26, pp. 843 to 853). Further, it is known that phagocytosis is decreased due to stress (Journal of UOEH, 1993, Vol. 15, pp. 161 to 171 and Neuroimmunomodulation, 2007, Vol. 14, pp. 4 to 7). Taken together the foregoing, it can be considered that it is useful to measure and evaluate phagocytic capacity of peripheral blood as an indicator of health status.
As a method for evaluating phagocytic capacity of phagocytes, for example, there are known a method of uptaking fluorescent latex beads into phagocytes and counting cells which have incorporated fluorescent latex beads under a fluorescent microscope, and a method of incorporating fluorescent latex beads into phagocytes and analyzing bead-incorporated cells using a flow cytometer (for example, Japanese Journal of Hygiene, April 2001, Vol. 56, No. 1, p. 315).